The disclosure relates to positioner systems having electronically commutated servomotors, wherein a position of an actuator that is to be positioned can be indicated by means of a position detector.
Numerous positioners are used in a motor vehicle. The positioners generally comprise an electrically motorized servomotor, a transmission or a mechanism and an actuator, the position of which actuator can be positioned by means of the servomotor and by way of the transmission. By way of example, positioners of this type can be used as throttle positioners, as an exhaust gas recirculation valve, for charge motion control valves and numerous comparable components.
Depending upon the field of application, positioners of this type are frequently provided with a position detector for indicating the actual position of the actuator. A position detector of this type can be used on the one hand to check the correct position of the actuator. As a consequence, it is possible to monitor that the controlled position of the positioner also corresponds to the actual position of the actuator. On the other hand, it is possible to control the position of the actuator with the aid of the actual position that is detected by means of the position detector, in that the measured actual position is controlled in comparison to the predetermined set position.
Brush commutated electric motors are generally used as servomotors for positioners of this type. However, said electric motors are encumbered by the disadvantage that their EMC behavior is impaired as a result of the development of brush sparking. Furthermore, said electric motors have a higher energy consumption owing to the friction of the brushes on a commutator and said electric motors have a reduced serviceable life owing to the wear on the brushes.
These disadvantages do not apply to electronically commutated electric motors that are used as servomotors. However, electronically commutated servomotors do require an external commutation, for which it is necessary to know the rotor position in order to ensure optimum commutation. The usual methods for ascertaining the rotor position use additional rotor position sensors in the electric motor, which sensors increase the overall production costs of the servomotor. In addition, the cost of providing cabling between the servomotor and the corresponding control device increases.
Methods that do not use sensors and are based for example on measuring the voltage that is induced in the stator winding, for example the back EMF method, also require a costly circuitry in the control device and are generally too expensive for positioners. Alternative methods that do not use sensors and wherein the rotor position is ascertained by means of measuring the rotor position of the dependent inductivity of the stator coils likewise require a costly circuitry in the control device and are in addition not as robust and as reliable as the methods that use sensors in order to measure the rotor position.
Positioner systems are known wherein the position detector that is arranged on the actuator or on the transmission that controls the actuator is used directly for commutating the brushless electric motor. The position variable that is provided by the position detector is converted into a rotor position in order to be able to use it during the commutation process.
When controlling the electronically commutated servomotor, the best level of efficiency with respect to torque is achieved when the motor magnetic field is advanced by 90° (electric rotor position) with respect to the exciter magnetic field, which exciter magnetic field is generated by the rotor of the servomotor. However, different influences, for example aging influences on the position detector, which have a drifting effect, and loss of accuracy owing to a reduction gear that couples the actuator to the servomotor, and its tolerances result in a reduced level of accuracy of the rotor position that is ascertained from the position variable. This can lead to the commutation of the servomotor being performed on the basis of an erroneous rotor position, so that only a reduced torque is available for the positioning process.
Since it is generally not certain that the position variable that has been ascertained by the position detector is allocated to the actual rotor position during the commissioning of the positioner system, it is necessary to perform a calibration process. A calibration process of this type can be performed for example by means of controlling the servomotor with the aid of commutation patterns in the controlled operation, said commutation patterns produce a defined direction of the motor magnetic field. In the controlled operation, the exciter magnetic field of the rotor is to be aligned with the motor magnetic field, so that the rotor position corresponds to the direction of the motor magnetic field. It is possible to allocate a position of the actuator to the rotor position that is ascertained in this manner.
Counter forces that are generally not constant take effect as the actuator is moved during the calibration process, said counter forces can be for example a result of friction or the like or also as a result of a restoring force that influences the actuator. These counter forces hamper the calibration process since they can cause an initially unknown deviation of the rotor position with respect to an actuator that is not influenced by counter forces.
It is therefore the object of the present disclosure to provide a method and a device for calibrating a positioner system whilst using an external position detector for the commutation process, which method compensates for the influence of non-constant counter forces on the actuator and/or the rotor.